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6.5
READ
(08
H )
BIT
BYTE
07
06
05
04
03
02
01
00
------1------1------1------1------1------1------1------
00
0
0
0
0
1
0
0
0
131
Logical unit Number
(MSB)
Logical Block Address
132
LogIcal Block Address
133
Logical Block Address
(LSB)
134
Number of Blocks
05
Reserved
(13)
1
Flag
1
Link
Figure 6-11.
READ Command
This command transfers from the ACB-5500 the specified number of
blocks starting at the specified logical starting block address
of the selected ST 506 drive.
The control unit will verify a valid seek address and proceed
to
seek to the specified starting logical block address.
If discon-
nection is allowed, the ACB-55130 will disconnect during seek
actuator motion and will reconnect when the device is again ready
to transfer data.
When the seek is complete the controller then
reads the data field into the buffer, checks ECC and begins first
data transfer to the Initiator.
Subsequent blocks of data are transferred into the buffer in a
similar manner until the block count is decremented to zero.
Cylinder switching is transparent to the user.
On a data ECC
error, the block is re-read up to 5 times to establish a solid
error syndrome.
Only then is correction attempted.
Correction
is done directly into the data buffer, transparent to the host.
Blocks containing uncorrectable data errors will be transferred
to the host prior to an ending check status.
A REQUEST sense
will return an uncorrectable data error (llH) error code.
500504-00
6-18
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